Emphasis has been placed on characterizing crystallin gene sequences in the chicken and the mouse. Alpha-, beta-, and gamma-crystallin cDNAs of the mouse have been cloned. Four different gamma-crystallin clones were obtained, suggesting a complex gene family for this protein. Sequencing studies showed that the alpha- and beta-crystallins are evolutionarily related proteins and that the principal beta-crystallin polypeptide of the mouse is internally duplicated. Restriction enzyme analysis indicated that the chicken delta-crystallin gene is hypomethylated at three sites when the gene is expressed in the lens; these sites are hypermethylated in cells that do not transcribe this gene. Studies with chickens and ducks showed a relationship between the structure of delta-crystallin mRNA and the ionic control of delta-crystallin synthesis observed earlier. Further evidence was obtained with galactosemic rat lenses that Na+ and K+ impair translation of crystallin mRNAs during the onset of osmotic cataracts. Finally, evidence was obtained for translational control of delta-crystallin mRNA during the maturation of embryonic chicken lens epithelial cells.